Aluminum support for planographic printing plates



United States Patent C Hill, NJ. No Drawing. Filed Oct. 1, 1964, Ser. No. 400,920 Claims priority, application Germany, Oct. 4, 1963,

v 15 Claims. c1. 96-1) Aluminum which is to be used as a support in the preparation of planographic printing plates requires a pretreatment to ensure good adhesion of the reproduction layer. Thus, bright aluminum has been mechanically treated in grain-ing machines with steel or plastic brushes in order to obtain a suitable support. However, lightsensitive layers do not adhere to the material treated in this manner to a degree which is desirable for the production of long runs. Alternatively, it has been suggested etch it with nitric acid, if desired, and then treat it with an aqueous solution of alkali silicates. Aluminum which has been pretreated in this manner has the disadvantage that only a few types of layers adhere thereto, i.e., negative-working light sensitive layers.

Further, aluminum has been pretreated by an electrolytic process prior to use in reproduction processes. However, the electrolytic process is very involves, particularly with regard to voltage supply for a continuous process and if wide aluminum webs are to be treated.

Printing plates are known which contain between the aluminum support and reproduction layer a thin intermediate layer consisting wholly or partially of at least one phosphonic acid and/or derivative thereof. In the present invention, an aluminum support for plano graphic printing plates has on at least one surface thereof a thin layer of mellitic acid to which, if desired, a reproduction layer may. be' applied.

For the preparation of the support of the present invention, commercially available aluminum, generally in the form of cut sheets, or, if a continuous process is used, in the form of a web, is coated on one or both surfaces with a mellitic acid layer. Known coating processes are used for this purpose; for instance, if both sides are to be coated, the aluminum may be immersed in cold or hot solutions of mellitic acid in water, in inorganic or in water-miscible organic solvents. If only one surface is to be coated, the mellitic acid solution may be applied by means of a whirler or by spraying.

Apart from solutions of mellitic acid in water, solutions in the following exemplary solvents, to which water is added, are also suitable: ketones, e.g. acetone; cyclic ethers, e.g. dioxane; or alcohols, e.g. methanol, ethanol or isopropanol; glycol ethers, e.g. ethylene glycol monomethly ether, or dimethyl formamide. Mixtures of these solvents may also be used.

If desired, the aluminum may be subjected to one of the known pre-cleansing processes prior to the application of the mellitic acid, using, e.g., hot alkali phosphate or alkali carbonate solutions, oxidizing agents, such as dilute nitric acid, and nitrate, chromate or hydrogen peroxide solutions. Alternatively, the aluminum may be precleaned cathodically or anodically by means of an electric current; however, in most cases, these precleaning methods are not necessary.

Coating time ranges from a few seconds to several minutes, depending on the quality of the aluminum foil, the temperature used and the concentration of mellitic acid. In most cases, a treatment of from 5 seconds to minutes, preferably 2 minutes to 5 minutes, at temperatures ranging from to 100 C. will be sufficient. The

3,301,574 Patented Jan. 31, 1967 "ice " concentration of the mellitic acid solution applied ranges to cleanse the aluminum surface with alkaline media, then from 0.01 to about 10 percent, preferably from 0.1 to 3 percent. It is also possible to increase the time of treatment and use solutions of higher or lower concentrations. However, operation outside of the stated ranges is often less advantageous and does not produce better results. If the aluminum sheets are treated by immersion, 1 percent solutions of mellitic acid in water or in water-miscible organic solvents may be used, for example. If mellitic acid is applied by means of a whirler, 0.1 to 2 percent solutions of the acid in one or more organic solvents are preferably employed.

To improve the hydrophilic properties of the aluminum surface, suitable additives may be incorporated in the mellitic acid solutions, in particular hydrophilic colloids, such as cellulose ethers, e.g. carboxy-methyl cellulose, hydroxyethyl cellulose, methyl cellulose, or alginates.

As a result of the treatment of aluminum with mellitic acid according to the present invention, even greasy, hydrophobic rolled aluminum becomes excellently hydrophilic.

The mellitic acid layer thus produced may be briefly rinsed with water and dried; drying at an elevated tem perature favorably influences the adhesion of the layers.

The aluminum support thus coated with mellitic acid maintains its hydrophilic properties for a long time and may be stored or shipped. A support provided with a hydrophilic surface in accordance with the present invention may be sensitized, by a known process, at a later date, usually immediately preceding printing. Alternatively, the desired reproduction coating may be applied immediately after the mellitic acid layer has been applied and dried. Thus, the mellitic acid coated aluminum may have a reproduction layer consisting of organic material, preferably in the form of a solution, applied thereto by hand or by means of a suitable coating device. Coating is effected in accordance with known methods, e.g., by immersion, roller application, or by spraying onto the rotating support; the solvent is then removed. Aluminum supports are obtained which are covered with a uniform, homogeneous layer and can be converted by known methods into plates which are ready for printing.

Suitable reproduction layers for the planographic printing plates of the present invention are layers in which image-wise differentiation can be produced by the influence of visible, ultraviolet, or infra-red light, X-rays, or heated bodies. Exemplary of such layers are: light-sensitive organic compounds, such as aliphatic and aromatic esters, hydrazides and amides of naphthoquinone diazide sulfonic acids; cinnamal-malonic acid and the substitution products and functional derivatives thereof; diazonium salts of amino-diphenylamine and their condensation products with formaldehyde; orthoand para-quinone di azides of benzene, anthracene or heterocyclic systems, e.g., of quinoline, indazole, benzimidazole, fiuorene and diphenylene oxide; diazo ketones; unsaturated ketones; ortho-' and para-aminoquinone diazides; derivatives of alkylnitronaphthalene sulfonic acids; nitroaldehydes; acenaphthenes; nitrones; stilbenes; azides; and diazides and diazo compounds of higher degrees of polymerization.

Also, reproduction layer with a high electrical resistance in the dark, which decreases by several powers of ten upon exposure to light or under the influence of heat, may be employed, such as those used in electrophotographic and electrothermographic processes, e.g., organic photoconductors of lower or higher molecular weights, if desired in admixture with resins. Oxadiazoles, imidazolones, triazoles, oxazoles, thiazoles, hydrazones, triazines, polyvinyl carbazoles, and polyvinyl oxazoles have proved to be particularly suitable photoconductors.

, Suitable resins are those having groups which render. them alkali-soluble, e.g., acid anhydride groups, carboxylic acid groups, sulfonic acid groups, sulfonamide groups or sulfonimide groups. Exemplary of such resins are: vinyl polymers and vinyl copolymers, phthalic acid ester resins, maleinate resins, alkyd resins, colophony resins and polyacrylic acid resins.

The aluminum supports of the present invention are advantageous in that, for practical purposes, all known types of reproduction layers adhere well to the mellitic acid surfaces and, after image-wise exposure and decoating of the image-free areas, which, depending on the reroduction layer employed, is effected with weak alkalis or with acids, they yield longer runs in offset printing machines than the hitherto used mechanically roughened aluminum foils. A further advantage of the supports of the present invention and of the planographic printing plates prepared therefrom is their ease of preparation, because in most cases commercial aluminum may be immediately subjected to the mellitic acid treatment in a bath.

The invention will be further illustrated by reference to the following specific examples:

Example 1.A mechanically roughened aluminum foil is immersed for 120 seconds at a temperature of 80 C. in a 1 percent by weight aqueous solution of mellitic acid. After drying, the foil is coated with a 1 percent by weight aqueous solution of the zinc chloride double salt of a diazo compound obtained by condensing 1 mole of 4- diazo-diphenylamine and 1 mole of formaldehyde in sulfuric acid. After exposure under a master, the diazo compound is removed from the unexposed areas by rinsing with water, and the image areas are inked up with greasy ink. Thereafter, printing can be performed as usual. The diazo compound above mentioned does not sufficiently adhere to mechanically roughened aluminum which was not pretreated with mellitic acid.

Example 2.An electrolytically roughened aluminum foil is immersed for minutes, at 90 C., in a 1.5 percent by weight aqueous solution of mellitic acid. After drying with warm air, the aluminum foil thus coated may be stored for several months without losing its favorable properties. After four months, the foil is sensitized by wiping it off with a 1 percent aqueous solution of a phosphate of a condensation product obtained from 3-methoxydiphenylamine-4-diazonium chloride and formaldehyde by condensation in 85 percent phosphoric acid. After exposure under a photographic negative, the entire foil is wiped over with a sponge soaked in water, whereby the layer is removed from the area not struck by light. Areas of the layer hardened by light are inked with greasy ink, whereas the mellitic acid layer adhering to the non-image areas of the aluminum repels ink. Printing can be performed as usual.

Example 3.A web of raw rolled aluminum is passed through a bath containing, by weight, 0.5 percent of mellitic acid and 0.01 percent of carboxymethyl cellulose in water maintained at a temperature of 95 C. It is then dried and coated with a 2 percent solution of 1-((4- methylbenzene 1 sulfonyl)-imino)-2-(2,5"-dimethyl-- ink and may then be used for printing in a printing machine.

Example 4.An aluminum foil is coated on a plate whirler with a solution containing, by Weight, 2 percent of mellitic acid, 88 percent of ethyleneglycol monomethyl ether, and 10 percent of water, dried,'coated, by the method described above, with a 1 percent by weight solution of 4-diazo-diphenylamine hydrochloride, and dried. After exposure under an original and removal of the layer from the unexposed parts 'by treatment with water, an image is obtained which is a negative with respect to the original used. After inking with greasy ink, printing can be performed.

Example 5 .An aluminum foil pretreated with mellitic acid according to the procedure of Example 1 is coated with a solution containing 1.5 percent by weight of 2,2- bis (naphthoquinone (1,2) diazide (2) sulfonyloxy-(S))-dinaphthyl-(l,l)-methane in ethylene glycol monoethyl ether. After exposure under a master, wiping over of the image surface with an approximately 5 percent trisodium phosphate solution, and inking with greasy ink, the resulting printing plate may be used for printing in a printing apparatus, direct images corresponding to the master being obtained.

Example 6.An aluminum foil is coated on a rotating plate whirler with a solution of 2 percent by weight of mellitic acid in a mixture consisting of percent of ethylene glycol monoethyl ether and 10 percent of water, dried, and then again coated, by the same method, with a 1 percent by weight solution of the naphthoquinone-( 1, 2)-diazide-(2)-5-sulfonic acid ester of phloroglucinol in ethylene glycol monoethyl ether, and dried with hot air.

After exposure under a diapositive and removal of the layer from the light-struck areas by wiping over with a cotton swab soaked in 3 percent trisodium phosphate solution, an image is obtained which is a positive with respect to the master used. Rinsing with water and about 1 percent phosphoric acid =and inking of the image areas with greasy ink are then performed.

Example 7.A mechanically roughened aluminum foil is immersed for 5 minutes at 50 C. in a 20 percent aqueous solution of trisodium phosphate and then for 5 minutes at 30 C. in a 1 percent by Weight aqueous solution of mellitic acid. After drying, the plate is coated with a solution containing 0.3 percent by weight of 2- phenylamino-3-oxethyl 5 cinnamylidene thiazolidone- (4), 0.3 percent of dicinn-amylidene-acetone, and 0.3 percent of a phenol resin modified with chloroacetic acid in ethylene glycol monomethyl ether. By exposure under a photographic negative, the light sensitive layer is hardened in the areas struck by light, and from the area-s not struck by light the layer is removed by wiping over with a solution containing 50 parts by weight of sodium metasilicate in a mixture consisting of 700 parts by volume of water, 500 parts by weight of triethylene glycol, and 200 parts by Weight of glycerine. The image areas are then inked up with greasy ink.

Example 8.An aluminum foil coated with mellitic acid as in Example 1 is coated with a solution containing 1 part by weight of 2,5-(4'-diethylamin-ophenyl-(1)- 1,3,4-oxadiazoile, 0.8 part by weight of a styrene copolymer containing carboxyl groups and having a specific gravi-ty of 1.26 to 1.28 and a decomposition range of 200 to 240 C., and 0.003 part by weight of Rhodamine B extra (Schultz Farbstotftabellen, 7th edition, vol. 1', No. 864) in 30 parts by volume of ethylene glycol monomethyl ether, and then dried. For the production of images on the electrocopying material thus obtained, the layer is given an electrostatic charge by means of a corona discharge and then exposed for one second under a master to a mercury lamp of watts. The electrostatic. image of the master thus obtained is made visible by dusting it over with a resin powder colored with carbon black and then fixed to form an electrophotographic copy which is resistant to rubbing by heating to C. For the preparation of a printing plate, the electrophotographic copy is wiped over with a solution consisting of 30 parts of methanol, 20 parts of glycerol, and 35 parts of ethylene glycol. The plate is then briefly rinsed with water and treated with an aqueous phosphoric acid solution of 0.5 to 5 percent concentration. After inking with greasy ink, the printing plate thus obtained may be used in the usual manner for printing in an offset machine, direct images corresponding to the master being obtained.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention Without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. A method for improving the receptivity for adhesively applied coatings of an aluminum surface which comprises treating the surface with a solution containing mellitic acid and drying to form a layer comprising mellitic acid on said surface.

2. A method according to claim 1 in which the solution is an aqueous solution.

3. A method according to claim 1 in which the solution is an aqueous solution containing an organic solvent.

4. A method according to claim 1 in which the concentration of mellitic acid in the solution is in the range of about 0.01 to percent.

5. A method according to claim 1 in which the solution contains, in addition, an additive to improve the hydrophilic properties of the aluminum surface.

6. An aluminum base having a layer comprising melllitic acid thereon.

7. An aluminum base having a layer thereon comprising mellitic acid and an additive to improve the hydrophilic properties of the aluminum surface.

8. An aluminum base having a first layer thereon comprising mellitic acid and a reproduction layer on the first layer.

9. An aluminum base according to claim 8 in which the reproduction layer is light-sensitive.

10. An aluminum base according to claim 8 in which the reproduction layer is photoconductive.

11. An aluminum base according to claim 9 in which the reproduction layer comprises a diazo compound.

12. A process for making a printing plate which comprises exposing a coated aluminum base to radiation under a master, the coating comprising a first layer comprising mellitic acid and a reproduction layer on the first layer, and developing the resulting image, whereby the coating is removed from the base material in the image-free areas thereof.

13. A process according to claim 12 in which the radiation is light.

14. A process according to claim 12 in which the reproduction layer is light-sensitive.

15. A process according to claim 12 in which the reproduction layer is phot-oconductive and is electrostatical'ly charged prior to exposure.

References Cited by the Examiner UNITED STATES PATENTS 2,560,137 7/1951 Slifkin 9675 2,918,416 12/1959 Taylor 204-58 OTHER REFERENCES Chemistry of Lithography, 1954, Lithographic Technical Foundation, Inc, New York 10, N.Y., pp. 103-106.

NORMAN G. TORCHIN, Primary Examiner.

ALEXANDER D. RICCI, Examiner. 

8. AN ALUMINUM BASE HAVING A FIRST LAYER THEREON COMPRISING MELLITIC ACID AND A REPRODUCTION LAYER ON THE FIRST LAYER.
 10. AN ALUMINUM BASE ACCORDING TO CLAIM 8 IN WHICH THE REPRODUCTION LAYER IS PHOTOCONDUCTIVE.
 12. A PROCESS FOR MAKING A PRINTING PLATE WHICH COMPRISES EXPOSING A COATED ALUMINUM BASE TO RADIATION UNDER A MASTER, THE COATING COMPRISING A FIRST LAYER COMPRISING MELLITE ACID AND A REPRODUCTION LAYER ON THE FIRST LAYER, AND DEVELOPING THE RESULTING IMAGE. WHEREBY THE COATING IS REMOVED FROM THE BASE MATERIAL IN THE IMAGE-FREE AREAS THEREOF. 